1. Field of the Invention
The present invention relates to exposure apparatus and methods used in photolithographic processes to produce, for example, semiconductor elements (e.g., chips), liquid crystal display elements, image pick-up elements (e.g., camera CCDs), thin film magnetic heads, and the like. The present invention is particularly applicable to scanning type exposure apparatus using a so-called step-and-scan method that successively exposes patterns on a mask onto each shot area on a photosensitive substrate while simultaneously moving (scanning) the mask and the substrate in synchronization in predetermined scanning directions.
2. Description of Related Art
Conventionally, a batch exposure type projective exposure apparatus, such as a stepper, has been used to manufacture semiconductor elements or the like using a photolithographic technology. Such apparatus expose images of patterns on a reticle used as a mask through a projective optical system and onto each shot area on a wafer (or a glass plate) on which photoresist or the like. has been applied. Typically, these projective exposure apparatus have used a so-called step-and-repeat method in which the entire pattern from the reticle is exposed onto the wafer shot area (i.e., the area where one chip. is formed) in one shot. The wafer is then stepped to the next position, and this process is repeated until the requisite number of shot areas on the wafer have been exposed. This process typically is repeated many times, using different reticle patterns to build up the various circuits, for example, on the plurality of chips formed on the wafer.
Difficulties have risen in using the step-and-repeat method due to the trend in the semiconductor industry to produce chips having larger sizes. Due to the larger size chips, the reticle patterns, and the resulting image that is exposed through the projective optical system, also has been made larger. This requires the exposure field of the projective optical system to be made larger, which causes the projective optical system to become more complicated in order to maintain aberrations within an allowable range throughout the entire exposure field. This increases the already high manufacturing cost, and causes the projective optical system to become large, which results in the entire body of the apparatus becoming too large.
In order to respond to the demand for increasing the area of the transferred pattern without enlarging the exposure field of the projective optical system, a scanning exposure type projective exposure apparatus using the so-called step-and-scan method has been developed. The step-and-scan method successively transfers and exposes patterns on a reticle onto each shot area on a wafer by scanning the reticle and the wafer synchronously with respect to the projective optical system so that, at any instant in time, a portion of the pattern of the reticle is projected onto the wafer through the projective optical system.
In the projective exposure apparatus, the patterns on the reticle are successively transferred to each shot area of the wafer by synchronizing and controlling a substrate (or wafer) stage that determines the position of the substrate and a reticle stage that determines the position of the reticle. Additionally, synchronizing and controlling of the substrate stage, an automatic focus (AF) system, a movable field diaphragm (a movable blind) in the illumination optical system, an exposure amount controlling mechanism, and the like are also performed. Any error that remains during exposure after performing the synchronization control (referred to hereafter as xe2x80x9ca synchronization control errorxe2x80x9d) causes a degradation of the transferred images or a registration error (i.e., an alignment error between a recently exposed image and an underlying image). Therefore, the various systems of the scanning exposure type projective exposure apparatus need to be dynamically controlled in parallel so that they are synchronized with respect to time (i.e., the timing by which they operate) and space (i.e., their position).
In the conventional scanning projective exposure apparatus, the patterns on the reticle are transferred onto each shot area on the substrate by synchronizing and dynamically controlling the reticle and substrate stage driving mechanisms, the automatic focus mechanism, the movable blind mechanism, the exposure amount control mechanism, and the like. However, small spatial and time synchronization control errors occur due to response speeds of the control systems that dynamically drive these various mechanisms, disturbances, and the like. Conventionally, an observation (that is, monitoring and storing) of the synchronization control errors that might occur during exposure is not specifically accomplished. When a shot area on which the pattern of the reticle is not accurately transferred due to an occurrence of a synchronization control error (referred to hereafter as xe2x80x9ca poor shotxe2x80x9d) occurs, the procedure simply moves to the next process (e.g., exposure of the next shot area) without recording the poor shot. Additional exposure (e.g., with different mask patterns) are performed, and the resulting chip is ultimately determined to be a poor chip, for example, after the chip is tested. Therefore, there is an inconvenience in that unnecessary exposures are performed on the poor shot area until the resulting chip is tested and determined to be a poor chip.
Moreover, the above poor shot could be selected as a sample shot when performing alignment in accordance with an enhanced global alignment (EGA) method, which creates further problems. As is known, the EGA method calculates arrangement coordinates of all shot areas on the wafer by using an alignment sensor that detects a position of an alignment mark on the wafer to measure a position of a plurality of sample shot areas selected from all shot areas on the wafer, and then statistically processes the measurement results. If the poor shot is selected, there is a possibility that position data of all shot areas will be significantly affected.
It is an object of embodiments of the present invention to provide a scanning type exposure apparatus that can reduce adverse effects to subsequent processes even when synchronization control errors occur.
In order to achieve the above and other objects, and to address the shortcomings in the prior art, a scanning exposure apparatus and method according to embodiments of the invention stores positional information relating to one or more areas on a substrate (e.g., a wafer) where one or more synchronization errors are detected to be greater than a predetermined value. The areas where the detected synchronization errors are greater than the predetermined value can then be eliminated from further exposure processing. Accordingly, throughput (productivity) is improved because time is not wasted exposing areas on the substrate that ultimately would yield defective devices (e.g., chips). Additionally, the areas where the detected synchronization errors are greater than the predetermined value can be eliminated from being used as sample areas during subsequent alignment processes, thereby avoiding the problems that can arise when such poor shot areas are used for alignment.
According to one embodiment of the invention, a scanning. exposure apparatus includes an illumination system a projection optical system a scanning system an error detecting system and a memory. The illumination system is located between a light source and a mask illuminated with light from the light source The projection optical system is located between the mask and a substrate and projects an image of an illuminated pattern from the mask onto the substrate. The scanning system synchronously moves the mask and the substrate so as to expose each of plural areas on the substrate with the pattern. The error detecting system detects an error in synchronous scanning of the mask and the substrate for each area. The memory stores positional information relating to one or more areas on the substrate where the detected error is more than the predetermined value.
The scanning system can include a mask stage that moves the mask relative to light from the light source, and a substrate stage that moves the substrate relative to light from the illuminated pattern. In such a case, the error detecting system can detect a positional error in synchronous movement of the mask stage and the substrate stage during scanning exposure of each area.
The scanning exposure system also can include an optical sensor that outputs a signal corresponding to a difference between an imaging plane of the projection optical system and the substrate in a direction along an optical axis of the projection optical system. For example, the optical sensor is part of an auto-focussing systems. In such a case, the error detecting system can also detect a focussing error in accordance with the signal output by the optical sensor.
The illumination system can include a stop member that is driven in response to movement of the mask relative to light output from the light source during scanning exposure. In such a case, the error detecting system can also detect an error in driving of the stop member.
The scanning exposure system also can include a light detector that outputs a signal corresponding to an intensity of light output by the light source and incident on the substrate. In such a case, the error detecting system can also detect an illuminance error in accordance with the signal output by the light detector.
The scanning exposure system also can include a display that indicates the one or more areas to be distinguished from other areas on the substrate. Additionally, a warning device can be provided that indicates when the errors exceed the predetermined value. for example, the warning device can indicate the location(s) of the area(s) on the substrate where the error(s) exceeded the predetermined value.
The memory can also store the synchronization control errors in correlation with the locations of the areas on the substrate the synchronization control errors were detected to be greater than the predetermined value
Another aspect of embodiments of the invention relates to a method of manufacturing a device using the scanning exposure apparatus. Such a method includes the steps of: synchronously moving a mask and a substrate so that each of plural areas on the substrate is exposed with a pattern from the mask; detecting an error in the synchronous moving of the mask and of the substrate for each of the areas; and exposing areas on the substrate for which the error is less than a predetermined value with another pattern, while eliminating areas on the substrate for which the error is greater than the predetermined value from exposure with the another pattern. The method can include the step of storing identifying information of one or more of the areas on the substrate for which the error is greater than the predetermined value so that, e.g., those areas can be eliminated from further processing. The error can include at least one of a positional error between the pattern and the substrate, an error in movement of a field stop that defines an illumination area on the mask, and an error in a light intensity in the illumination area. The error can also include a positional error between each area and the pattern, at least one of a focussing error in a direction along an optical axis of the projection optical system, and an alignment error in a plane perpendicular to the optical axis.